At present, batching is widely used in the laboratories of various brances of science and industry as a basic operation included into such processes as pipetting, mixing, diluting, sampling for analyses, fractionation, preparation of samples for analyses.
Known in the prior art is a peristaltic batcher (see Author's Certificate No. 570778 Int.Cl..sup.2 G01F 13/00, USSR) comprising an elastic hose with a movable portion and immovable portions, an electric drive motor with a shaft for rolling the movable portion of the elastic hose, a roller for pressing the movable portion of the elastic hose against the electric motor shaft, a squeezing means installed on one of the immovable portions of the elastic hose, a drive for moving the roller and the squeezing means, two transmitters indicating the terminal position of the movable portion of the elastic hose, and a control unit incorporating a reversing device connected electrically with the electric motor, with the drive and with the terminal position transmitters, and a pulse-controlled cut-in switch connected with the reversing device and having an input which serves as the starting input of the control unit. The elastic hose in this batcher is arranged in the shape of a single loop whose immovable portion passes between a clamp intended to change the size of the single loop, and a stop.
However, a rise of counterpressure of the handled medium in this batcher is accompanied by the growing resistance to the rolling of the hose so that it slips on the electric motor shaft whereby the reliability of batching is impaired.
Besides, this batcher can operate in one mode only, viz., in the single-batch mode in which the batcher discharges one single batch per each pulse delivered to the starting input, said single batch being directly proportional to the diameter and length of the rolled portion of the elastic hose which limits the batching range.
Besides, alternating discharge and suction batching required, say, in the process of pipetting calls in this batcher for exchanging the ends of the hose because this batcher is capable of working in one direction only which hampers its employment in laboratories.
Furthermore, the single-loop arrangement of the hose in this batcher creates a twisting force directed along the hose generatrix which increases the danger of small-diameter hose breaking contact with the electric motor shaft.
And, finally, the inward and outward movement of the elastic hose in the clamp of this batcher for changing the size of the single loop is not measured quantitatively, which hinders setting and correcting the size of a single batch.